RE: VisioToCoreModelImport.xslt

First, export your Visio model to XML using Orthogonal Toolbox, available from http://www.orthogonalsoftware.com/products.html
After that, all you need to do is open that XML file in Visual Studio, and it should automatically be converted and opened by NORMA. To be able to save that file, you will need to do a 'Save As' first. We require this so that users don't accidentally save over their original copy of the model without realizing it.

RE: VisioToCoreModelImport.xslt

My apologies, I forgot to mention one of the required steps.
In the Open File dialog, select the XML file exported from Visio. Then, click on the down arrow glyph on the right of the "Open" button. Select "Open With...", and a list of different editors should appear. Select "ORM Designer" from this list, and press "OK".

RE: VisioToCoreModelImport.xslt

Hmm, something would seem to be not working correctly.
Try opening the Visio.xml file in Studio's regular XML editor. Then, from the "XML" menu, choose "Show XSLT Output". It should prompt you whether you want to specify a stylesheet. Click yes, and browse to the "VisioToCoreModelImport.xslt" file.
Studio should then run the transform again your model file, and open the result in a new document window. What does the result like? Is it empty?

RE: VisioToCoreModelImport.xslt

At the current time, probably not.
As far as I know, Visio treats all the pages as part of a single model, and Orthogonal Toolbox only exports that backend model information, not the diagram, paging, and layout information.